Microwave ablation generator control system

ABSTRACT

A microwave energy delivery and measurement system, including a microwave generator and a microwave energy delivery device, for performing medical procedures, and a remote power coupler system for measuring one or more parameters of the microwave energy signal including a remote RF sensor housed in the microwave energy delivery device and a power coupler processer coupled with the processing unit of the microwave energy delivery device.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15/182,269, filed on Jun. 14, 2016, which is a continuation of U.S.application Ser. No. 14/636,708, filed on Mar. 3, 2015, now U.S. Pat.No. 9,375,277, which is a continuation of U.S. application Ser. No.13/419,981, filed Mar. 14, 2012, now U.S. Pat. No. 8,968,290, the entirecontents of each of which are incorporated by reference herein.

BACKGROUND 1. Technical Field

The present invention relates to systems, devices and methods forperforming a medical procedure, wherein the system, apparatus and methodincludes the measurement of at least one parameter related to themicrowave energy delivered to the handpiece of the microwave energydelivery device.

2. Description of Related Art

During microwave ablation procedures, the electrical performance of themicrowave energy delivery system (e.g., the system including agenerator, a microwave energy delivery device, a waveguide configured todelivery the microwave energy signal from the generator to the handpieceof the device, and an antenna) changes throughout the course of anablation treatment. The change in performance may be due to a change inthe delivery device, a change in the tissue properties or a change inthe delivery path. The ability to observe parameters indicative of thesechanges provides better control of the delivery of the microwave energy.

For example, measuring antenna impedance is a common method fordetermining antenna performance and/or a change in an antenna property.Microwave systems are typically designed to a characteristic impedance,such as, for example, 50 Ohms, wherein the impedance of the generator,the delivery system, the ablation device and tissue are about equal tothe characteristic impedance. Efficiency of energy delivery decreaseswhen the impedance of any portion of the system changes.

With low frequency RF systems impedance can easily be determined bymeasuring the delivered current at a known voltage and calculatingtissue impedance using well known algorithms. Obtaining accuratemeasurements of tissue impedance at microwave frequencies is moredifficult because circuits behave differently at microwave frequency.For example, unlike an electrode in an RF system, an antenna in amicrowave system does not conduct current to tissue. In addition, othercomponents in a microwave system may transmit or radiate energy, like anantenna, or components may reflect energy back into the generator. Assuch, it is difficult to determine what percentage of the energygenerated by the microwave generator is actually delivered to tissue,and conventional algorithms for tissue impedance are typicallyinaccurate.

Therefore, other methods of measuring impedance are typically used in amicrowave system. One well known method is an indirect method usingmeasurements of forward and reverse power. While this is a generallyaccepted method, this method can also prove to be inaccurate because themethod fails to account for component losses and depends on indirectmeasurements, such as, for example forward and reverse powermeasurements from directional couplers, to calculate impedance. Inaddition, this method does not provide information related to phase, acomponent vital to determining antenna impedance.

The present disclosure describes a microwave energy delivery system thatincludes a microwave energy delivery device configured to measure atleast one parameter related to the energy delivered to the handpiece ofthe microwave energy delivery device.

SUMMARY

The present disclosure relates to a microwave energy delivery andmeasurement system, including a microwave generator and a microwaveenergy delivery device, for performing medical procedures. In one aspectof the invention, the microwave energy delivery and measurement systemincludes a microwave generator for delivery of a microwave energy signaland a microwave energy delivery device configured to receive themicrowave energy signal. The microwave generator includes a processingunit configured to control the generation and delivery of the microwaveenergy signal at a predetermined microwave frequency and configured toreceive one or more measurement signals, related to the microwave energysignal, from the microwave energy delivery device. The microwavegenerator also includes a directional coupler configured to generate andprovide one or more generator measurement signals related to forwardpower and/or reverse power of the microwave energy signal at themicrowave generator to the processing unit. The microwave energy deliverdevice includes a housing, a microwave antenna coupled to the housingand configured to receive the microwave energy signal and resonate atthe predetermined microwave frequency, a remote RF sensor and a remotesensing interface. The remote RF sensor is disposed in the housing,coupled to the microwave antenna and configured to generate and provideone or more remote measurement signals. The remote sensing interface iscoupled between the processing unit of the microwave generator and theremote RF sensor. The remote sensing interface is configured to receiveone or more remote measurement signals from the remote RF sensor and toprovide remote measurement signals to the processing unit.

In other aspects of the present disclosure, the remote RF sensor mayinclude a remote directional coupler. Further, a remote measurementsignal from the remote sensing interface may be related to forward powerand/or reverse power of the microwave energy signal at the remotedirectional coupler.

In other aspects of the present disclosure, the remote sensing interfacemay include one or more conductors coupled between the microwave energydelivery device and the microwave generator or the remote sensinginterface may generate a wireless connection between the microwaveenergy delivery device and the microwave generator.

In other aspects of the present disclosure, the processing unit may beconfigured to adjust a parameter related to the microwave energy signalbased on a property of a generator measurement signal and/or a remotemeasurement signal. The processing unit may include a comparatorconfigured to generate a comparator signal related to a comparison of agenerator measurement signal and a remote measurement signal. Thegenerator measurement signals and/or the remote measurement signals maybe related to forward power and/or related to reverse power.

In other aspects of the present disclosure, the remote RF sensor mayinclude a remote directional coupler and an intermediate frequencygenerator connected to the remote directional coupler. The remotedirectional coupler may be configured to generate an unconditionedmeasurement signal at a predetermined frequency related to the microwaveenergy signal. The intermediate frequency generator connected to theremote directional coupler is configured to mix each of theunconditioned measurement signals with a carrier signal therebygenerating an intermediate measurement signal related to eachmeasurement signal generated by the remote directional coupler.

In other aspects of the present disclosure, the intermediate frequencygenerator may include an oscillator and a power mixer. The oscillatormay be configured to generate the carrier signal at a carrier signalfrequency. The power mixer may be configured to generate an intermediatemeasurement signal by mixing the carrier signal and a unconditionedmeasurement signal generated by the remote directional coupler. Theremote measurement signal provided by the remote RF sensor interface tothe microwave generator may include an intermediate measurement signalgenerated by the power mixer.

In other aspects of the present disclosure, the processing unit mayinclude an electrosurgical generator processing unit and a remote powercoupler processing unit. The electrosurgical generator processing unitmay be configured to control the generation and delivery of themicrowave energy signal at the predetermined microwave frequency. Theremote power coupler processing unit may be configured to receive aremote measurement signal related to the microwave energy signal andconfigured to provide the remote measurement signal to theelectrosurgical generator processing unit. In one aspect of the presentdisclosure, the remote power coupler processing unit is an add-on deviceincorporated into an electrosurgical generator.

Aspects of the present disclosure may include a light-weight directionalcoupler for measuring a property of a microwave energy signal. Thelight-weight directional coupler may include a through-signal coaxialcable and a coupled coaxial cable, each including an inner conductor andan outer conductor formed in a coaxial relationship, abutting andparallel to each other along a length thereof. The through-signalcoaxial cable and the coupled coaxial cable each define a first slothaving a first length and a second slot having a second length therein.The first and second slots are adjacent each other to operatively couplethe through-signal coaxial cable and the coupled coaxial cables to eachother.

In other aspects of the present disclosure, each slot may be formed byremoving a portion of the outer conductor thereby forming ahalf-cylinder opening at each slot. The slot length of each of the firstslot and the second slot may be equal and the spacing between the firstslot and the second slot along the length may be equal. The spacingbetween the first slot and the second slot may be equal to one-quarterof a wavelength (λ/4) of the microwave energy signal provided to thethrough-signal coaxial cable. The first slot length and the second slotlength may be between 13 mm and 15 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of the present disclosure are described hereinbelow withreference to the drawings, wherein:

FIG. 1 is a perspective view of microwave energy delivery systemaccording to an embodiment of the present disclosure;

FIG. 2 is a control circuit, electrical block diagram of a typicalelectrosurgical generator;

FIG. 3 is a control circuit, electrical block diagram of a microwaveenergy delivery system according to an embodiment of the presentdisclosure;

FIG. 4A is a perspective view of the microwave energy delivery deviceincluding a compact remote directional coupler;

FIG. 4B is an exploded view of the microwave energy delivery deviceincluding a compact remote directional coupler of FIG. 4A; and

FIG. 5 is a functional block diagram of a remote directional coupleraccording to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Detailed embodiments of the present disclosure are described herein;however, it is to be understood that the disclosed embodiments aremerely exemplary and may be embodied in various forms. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a basis for the claims and asa representative basis for teaching one skilled in the art to employ thepresent disclosure in virtually any appropriately detailed structure.

In the drawings and in the descriptions that follow, the term“proximal,” as is traditional, will refer to an end which is closer tothe user, while the term “distal” will refer to an end that is fartherfrom the user.

Referring now to FIG. 1, a system for supplying microwave energy formicrowave therapy, according to an embodiment of the present disclosure,is shown as 10. The microwave energy delivery system 10 includes anelectrosurgical generator 20 with a control circuit 22 for controllingthe operation of the electrosurgical generator 20 and a microwave energydelivery device 30 coupled to the electrosurgical generator 20 via atransmission line 34.

Transmission line 34 includes a coaxial cable 34 a (i.e., a waveguide)and an auxiliary cable 34 b. The coaxial cable 34 a is configured todeliver a microwave energy signal between the electrosurgical generator20 and the handpiece 36 of the microwave energy delivery device 30. Theauxiliary cable 34 b is configured to deliver one or more signalsbetween the handpiece 36 and the electrosurgical generator 20. The oneor more signals delivered between the handpiece 36 and theelectrosurgical generator 20 may include a DC power signal for poweringcircuitry in the handpiece 36 and an information signal containingreal-time or historical information related to a condition and/or aquality of the microwave energy signal at the handpiece 36, the shaft 38(extending from the handpiece 36) and/or the antenna 32 (on the distalend of the microwave energy delivery device 30) that radiatestherapeutic energy therefrom.

A transmission line connector 24 disposed on the proximal end of thetransmission line 34 connects to a transmission line receiver 46 on theelectrosurgical generator 20. A distal end of the transmission line 34connects to the microwave energy delivery device 30.

Electrosurgical generator 20 may include an operator interface 40 havinga keypad 42 for entering parameters related to electrosurgical generator20, the microwave energy delivery device 10 and/or parameters related tothe delivery of microwave energy. Display 44 may indicate or graph oneor more parameters related to the delivery of microwave energy and/orone or more parameters related to the microwave generator 20,transmission line 34 and/or microwave energy delivery device 10.

Microwave energy delivery device 30 includes handpiece 36, shaft 38 andantenna 32 formed on the distal end of the shaft 38. One suitablemicrowave energy delivery device 30, as illustrated in FIG. 1, is atissue penetrating microwave energy delivery device 30 sold by Covidienunder the trademark Evident™ Microwave Ablation Surgical Antennasalthough the embodiments described herein may be suitable for any devicecapable of delivering microwave energy or the like. The embodimentsdescribed herein may also be applied to any suitable energy deliverydevice as explained in more detail below.

Referring to FIG. 2, the control circuit, electrical block diagram of atypical electrosurgical generator 20 is shown generally designatedcontrol circuit 100. For clarity, the control circuit 100 of theelectrosurgical generator 20 only provides the general functionality ofa control circuit of a typical microwave generator 20 and does notinclude all aspects of a microwave generator 20. The functionality ofindividual components may be combined or included in one or morecomponents and the various components are interconnected with suitablecables and/or connectors.

The control circuit 100 includes a signal generator 105 capable ofgenerating and supplying a high frequency microwave signal to anamplifier 110. Signal generator 105 may be a single frequency generator,may include variable frequency capability or may include the capabilityof providing a signal that includes two or more related frequencieswherein the microwave energy delivery device 30 (See FIG. 1) isconfigured to resonate at the two or more related or unrelatedfrequencies.

Amplifier 110 receives and amplifies the high frequency microwave signalfrom the signal generator 105 to a desirable energy level. Amplifier 110may include a single-stage or multi-stage amplifier and may include oneor more signal conditioning circuits or filters (not shown) such as, forexample, a low-pass filter circuit, a high-pass filter circuit or abandpass filter circuit. Amplifier 110 gain may be fixed or controlledby a suitable controller, such as, for example, a control algorithm inthe supervisory control system (not shown), a central processing unit120 (CPU) or the gain of the amplifier 110 may be manually adjusted by aclinician through the keypad 42 (See FIG. 1).

Amplifier 110 supplies a continuous, amplified microwave signal to a hotswitch relay 125. Hot switch relay 125 is controlled by the CPU 120 andconfigured to switch the amplified microwave signal to one of anamplifier burn-off load resistor 130 and a circulator 135. For example,in position A the hot switch relay 125 delivers energy to burn-off loadresistor 130 and in position B delivers energy to the circulator 135.

Hot switch relay 125 may be any suitable solid-state high power switchcapable of switching a high power microwave energy signal. Hot switchrelay 125 receives the high power microwave signal from the signalgenerator 105 and amplifier 110, and passes the signal between theamplifier burn-off load resistor 130 and the circulator 135 withoutpowering down the signal generator 105 or amplifier 110. In use, the hotswitch relay 125 allows the electrosurgical generator 20 to provide nearinstantaneous power (e.g., can provide nearly continuous power with veryrapid on/off capabilities) without creating amplifier transients, byeliminating the need to power down the signal generator 105 or amplifier110.

Amplifier burn-off load resistor 130 may be any suitable coaxialterminator capable of dissipating microwave energy while generating aminimal amount of voltage standing wave ratio (VSWR), or reflectiveenergy, over the bandwidth of the signal generator 105.

Circulator 135 is a passive three port device that eliminates standingwaves between the hot switch relay 125 and the directional coupler 145.Circulator 135 passes signals received on Port A to Port B, signalsreceived on Port B to Port C and signals received on Port C to Port A.When hot switch relay 125 is in Position A, the microwave energy signalis passed from Port A of the circulator 135 to the directional coupler145 connected to Port B. Reflected energy from the directional coupler145 (e.g., the transmission line receiver 146 connected to thetransmission line 134 and the microwave energy delivery device 130)received on Port B, is passed to Port C and dissipated through thereverse energy burn-off load resistor 142. Reverse energy burn-off loadresistor 142 is similar in function to the amplifier burn-off loadresistor 130 as discussed hereinabove.

Directional coupler 145 may be configured to operate like mostconventional directional couplers known in the available art.Directional coupler 145 passes the high power microwave energy signalreceived on Port 1 to Port 2 with minimal insertion loss. Energy isreflected back through the transmission line receiver 46 (from thetransmission line 134 and microwave energy delivery device 30) andreceived on Port 2 of the directional coupler 145, passed through thedirectional coupler 145 and out Port 1 of the directional coupler 145,and to Port B of the circulator 135. Circulator 135 passes the energyreceived through Port B to Port C of the circulator 135 and the energyis dissipated by the reverse energy burn-off load resistor 142.

Directional coupler 145 samples a small portion of each of the signalsreceived on Port 1 and Port 2 and passes the small portion of eachsignal to Ports 3 and 4, respectively. The signals on Port 3 and 4 areproportional to the forward and reverse power, respectively, andprovided to the CPU 120.

The forward and reverse power signals from the directional coupler 145are measured by a measurement system (e.g., contained in the CPU 120)configured to obtain samples of the signals. The measurements are takencontinuously or periodically, thereby providing an indirect measurementof the delivered energy (i.e., forward power) and the reflected energy(reverse power). These power measurements from a directional coupler 145positioned in the microwave generator 20 are limited to characteristicsof the microwave energy signal supplied to the transmission linereceiver 146 and are not necessarily the same characteristics of themicrowave energy signal received by the microwave energy delivery device30 and not necessarily the same characteristics of the microwave energysignal delivered to patient tissue by the antenna 32.

FIG. 3 is a control circuit block diagram of a microwave energy deliverysystem according to an embodiment of the present disclosure and isgenerally designated as 200. For clarity, the control circuit blockdiagram 200 of the electrosurgical generator 20 only provides generalfunctionality and does not include all aspects of a microwave generator20. The functionality of individual components may be combined orincluded in one or more components and the various components areinterconnected with suitable cables and/or connectors.

The control circuit block diagram 200 includes components in theelectrosurgical generator 220 and components in the microwave energydelivery device 230 connected through the transmission line 234.Transmission line connector 224 on the proximal end of the transmissionline 234 connects to the transmission line receiver 246 on theelectrosurgical generator 220 and the distal end of the transmissionline 234 connects to the microwave energy delivery device 230.Transmission line 234 includes a coaxial cable 234 a for transmittingthe microwave energy signal between the microwave generator 220 and themicrowave energy delivery device 230 and an auxiliary cable 234 b. Theauxiliary cable 234 b may include a remote RF power cable (DC Power), aforward measurement signal cable, a reverse measurement signal cablesand an information signal cable for transmitting real-time or historicalinformation related to a condition and/or the quality of the microwavesignal in the microwave energy delivery device 230.

The microwave generator 220 includes a processing unit (CPU 120)configured to control the generation and delivery of a microwave energysignal at a predetermined microwave frequency. The CPU 120 is furtherconfigured to receive measurement signals related to the microwaveenergy signal at various locations in the microwave energy deliverysystem. For example, the CPU 120 receives a measurement signal relatedto the microwave energy signal within the microwave generator 220 fromthe dual directional coupler 145 housed in the microwave generator 220and also receives a measurement signal related the microwave energysignal within the microwave energy delivery device 230 from a remote RFsensor 260 b. The CPU 120, by receiving information related to themicrowave energy at various locations in the delivery path, is able todetermine energy losses at various locations in the system and mayperform adjustments to the microwave energy signal based on theinformation received. The measurement signals generated by thedirectional coupler 145 and the remote RF sensor 260 b may be related toforward power, reverse power, forward and reverse power as discussed indetail hereinbelow.

The functional blocks of the remote power coupler system 260 includesthe power coupler processor 260 a and the remote RF sensor 260 b. Theremote RF sensor 260 b is housed in the microwave energy delivery device230 and includes a remote directional coupler 245, a remote oscillator265, a remote power splitter 266, remote forward power mixer 263 andremote reverse power mixer 264, remote forward intermediate signaltransmitter 268 and remote reverse intermediate signal transmitter 269.The individual components of the remote RF sensor 260 b and theirfunctionality may be performed by a single device or component. RemoteRF sensor 260 b is positioned between the transmission line 234 and theantenna 232 and may be housed in the handpiece 336 (as illustrated inFIG. 4a ) or housed in the shaft 238.

The remote power coupler processor 260 a is housed in and/or directlyconnected to the electrosurgical generator 220 and coupled to the remoteRF sensor 260 b. The remote RF sensor 260 b generates one or moresignals related to the microwave energy signal that passes through theremote RF sensor 260 b. The signals generated by the remote RF sensor260 b are directly or indirectly provided to the remote power couplerprocessor 260 a (e.g., wirelessly transmitted or transmitted via one ormore conductors in the remote sensing interface cable 234 b). The remotepower coupler processor 260 a processes the signals and/or data from theremote RF sensor 260 b and provides the characteristics, signals and/orvalues related to the measured microwave energy signal (e.g., the signalprovided to the remote RF sensor 260 b) to the CPU 120 in theelectrosurgical generator 220.

In one embodiment, the remote power coupler processor 260 a is aninternal or external plug-in card and/or add-on device that may beincorporated into the electrosurgical generator 220. For example, remotepower coupler processor 260 a may be removably connected to a port suchas, for example, a serial data port, a communication port or a directbus connection port. In another embodiment, the functionality of theremote power coupler processor 260 a is incorporated into the CPU 120 ofthe electrosurgical generator 220.

The remote directional coupler 245 proportionally divides the forwardpower microwave energy signal, generated by the electrosurgicalgenerator 220 and provided to Port 1, between an unconditioned forwardpower measurement signal on Port 3 and a forward microwave energy signalon Port 2. The forward power measurement signal on Port 3 is provided toa forward power mixer 263 and the forward energy signal on Port 2 isprovided to the antenna 232. The unconditioned forward power measurementsignal is converted, conditioned and provided to the remote powercoupler processor 260 a as discussed hereinbelow.

At least a portion of the forward microwave energy signal from Port 2 isreflected back from the transmission path between Port 2 and/or theantenna 232. The reflected energy (e.g., the reverse signal) is providedto Port 2 and a portion of the reverse signal is proportionally dividedbetween an unconditioned reverse power measurement signal on Port 4 anda reverse microwave energy signal on Port 1. The unconditioned reversepower measurement signal on Port 4 is provided to a forward power mixer264 and converted, conditioned and provided to the remote power couplerprocessor 260 a as discussed hereinbelow.

The forward and reverse power mixers 263 and 264 receive a carriersignal, generated by the oscillator 265 and split by the power splitter266. The forward and reverse power mixers 263 and 264 also receive therespective unconditioned forward and reverse power measurement signalfrom the remote directional coupler 245. The forward and reverse powermixers 263, 264 each mix the carrier signal with the respectiveunconditioned forward and reverse power measurement signals therebydown-converting the unconditioned forward and reverse measurementssignals to forward and reverse intermediate frequency IF signals in thekHz range. For example, as illustrated in FIG. 3, the remote RF sensor260 b may be configured to down-convert the unconditioned forward andreverse measurement signals from 915 MHz to an IF signal frequency of100 kHz using a carrier signal of 915 MHz.

The forward and reverse IF signals from the mixers 263 and 264 areprovided to the forward and reverse power transmitters 268 and 269,respectively, and are transmitted to the remote power coupler processor260 a. Signals may be transmitted via one or more conductors in theremote sensing interface cable 234 b or signals may be digitized by theforward and reverse power transmitters and wirelessly transmitted to theremote power coupler processor 260 a. Power transmitters 268 and 269 maycondition the forward and reverse IF signals by filtering and/oramplifying the forward and reverse IF signals prior to transmission.Power transmitters 268 and 269 may be configured to transmit informationrelated to the forward and reverse IF signals to the remote powercoupler processor 260 a (e.g., gains values and information related tothe carrier signal). The information from the power transmitters 268,269 may be conveyed through a separate information signal cable includedas part of the auxiliary cable 234 b, added to the forward and reverseIF signals or wirelessly transmitted to the remote power couplerprocessor 260 a.

The remote power coupler processor 260 a converts the forward andreverse IF signals to a digital signal, extracts information from thedigital signals and/or the conveyed information and provides theextracted information to the CPU 120 of the electrosurgical generator20. The extracted information may include signal amplitude, phaseinformation, phase relationships information (e.g., phase relationshipbetween the forward and the reflected signals) and/or reflectioncoefficients.

In one embodiment, a pre-measurement calibration procedure calibratesthe remote directional coupler 245 prior to delivering energy to patienttissue. The pre-measurement calibration procedure may include performingmeasurements under various loaded and/or unloaded conditions (e.g.,short, open and matched load conditions). Measurements from one or bothdirectional couplers 145, 245 during the pre-measurement calibrationprocedure may be used in the electrosurgical energy delivery algorithmand/or the control algorithm. Alternatively, in another embodiment thecalibration of the remote directional coupler 245 may allow thedirectional coupler 145 in the electrosurgical generator 220 to betemporarily bypassed and/or eliminated.

In yet another embodiment, a calibration procedure that calibrates (orre-calibrates) the remote directional coupler 245 is performed duringthe energy delivery procedure or as a step in the electrosurgical energydelivery control algorithm and/or the control algorithm.

Electrosurgical generator 220 may modify, pause or terminate energydelivery if one or more measurements or values from the remote powercoupler system 260 exceed a threshold, the difference between one ormore values exceeds a threshold or a changing in a value exceeds athreshold. In another embodiment, the electrosurgical generator 220determines the viability (e.g., useful life and/or expected life) of oneor more components of the electrosurgical system, such as, for example,the viability of the cable 334, the viability of microwave energydelivery device 330 and/or the viability of one or more componentsthereof.

In another embodiment, the CPU 120 utilizes a measurement, data or asignal from the remote power coupler system 260 (power coupler processor260 a and/or remote RF sensor 260 b) to determine a change in thecondition of the energy delivery pathway and/or change in the conditionof the target tissue. For example, the CPU 120 may determine that achange occurred in one or more parameters or the CPU 120 may determinethat a change in the rate of change occurred in one or more parameters.The change may indicate a condition, may indicate a change in thetissue, may indicate a change in a tissue property and/or may be used topredetermine or predict a condition. The CPU 120 may use the calculatedchange or calculated rate of change to modify an operation parameter, tomodify an energy delivery parameter and/or to determine the viability ofone or more components of the electro surgical system.

In another embodiment the use of the change of a parameter, the rate ofchange of a parameter, and/or the comparison of a change and/or a rateof change of a parameter at the directional coupler 145 and/or theremote RF sensor 260 b may eliminate the need to calibrate the remotedirectional coupler 245 since the actual value is irrelevant and usedonly to determine if a change has occurred. For example, when energydelivery is initiated, the CPU 120 may record an initial snapshot of themicrowave energy signal (e.g., the various parameters related to themicrowave energy signal) at the directional coupler 145 and at theremote RF sensor 260 b. The initial snapshot may be used as an energydelivery baseline to determine any changes in delivered energy or anychanges in the energy delivery pathway.

In another embodiment, the CPU 120 compares the change of the forwardpower measured at the directional coupler 145 to the change of theforward power at the remote RF sensor 260 b to determine if the powerloss, or rate of power loss, at the electrosurgical generator 220 variesfrom the measurements at the remote RF sensor 260 b. The CPU 120 mayalso compare the calculated change of the reverse power, measured at thedirection coupler 145, to the calculated change of the reverse power,measured at the remote RF sensor 260 b. The comparison may determine ifthe change in the reflected power at the directional coupler 145 variesfrom the change in the reflected power at the remote RF sensor 260 b.

In another embodiment, the CPU 120 compares the calculated rate ofchange of the reverse power measurement at the remote directionalcoupler 245 to the calculated rate of change of the forward powermeasurement at the remote RF sensor 260 b to measure a rapidly changingevent, such as a change in tissue property. Change in tissue propertywill be observed through a change in reflected power at both directionalcouplers 145 and 245. The comparison may also be used to predict acondition and to control energy delivery based on the prediction. Byusing the change or rate of change, the relative accuracy of themeasurements is not relevant to measurements of change or measurementsof the rate of change.

In another embodiment, the CPU 120 compares the forward powermeasurement at the remote directional coupler 245 with the forward powermeasurement at the directional coupler 145 to determine the forwardpower losses in the cable 234 a or to determine a change in the forwardpower losses in the cable 234 a. Additionally, or alternatively, the CPUmay compare the reverse power measurement at the remote directionalcoupler 245 with the reverse power measurement at the directionalcoupler 145 to determine a change in the reverse power losses in thecable 234 a or to determine a change in the reverse power losses in thecable 234 a.

Another embodiment of the present disclosure is a lightweight coaxialcoupler suitable for placement and use in the handpiece 336 of amicrowave energy delivery device 230. A commonly used coaxial coupler,manufactured and sold from MECA Electronics of Denville, N.J., is ratedfor a maximum power of 500 W, has a directivity of 25 dB and a couplingof 30 dB and weighs approximately 1 pound. As such, this commonly usedcoaxial coupler, while providing the desired functionality for theremote directional coupler, may not be commercially successful becauseof the additional and excessive weight the commonly used coaxial couplerwould add to the microwave energy delivery device 230.

FIG. 4A is a perspective view and FIG. 4B is an exploded view of amicrowave energy delivery device 330 including a light-weight remotedirectional coupler 345 according to another embodiment of the presentdisclosure. The light-weight remote directional coupler 345, which ispart of the remote power coupler system 260 discussed hereinabove, isintegrated into the handpiece 336. The space requirements of thelight-weight remote directional coupler 345 may require slight or noenlargement of the handpiece 336 and adds approximately 100 grams to theoverall weight of the microwave energy delivery device 330 therebymaking the addition of a remote power coupler system 260, describedhereinabove, a feasible addition to any microwave energy deliverysystem.

As illustrated in FIG. 4B, the light-weight remote directional coupler345 includes a through-signal coaxial cable 345 a and a coupled coaxialcable 345 b. The through-signal coaxial cable 345 a is part of, orconnects to, the shaft 338 and receives a microwave energy signal fromthe coaxial cable 334 a of the transmission line 334. The coupledcoaxial cable 345 b connects to the remote forward and reverse mixers363, 364. The remote forward and reverse power mixers 363, 364 connectto the remote power splitter 366 and receive a carrier signal generatedby the remote oscillator 365 therefrom. In use, the light-weight remotedirectional coupler 345 provides a forward power measurement signal anda reverse power measurement signal to the respective mixer 363 and 364.The mixers 363 and 364 down-converts the respective measurement signalusing the carrier signal and the down-converted signals are provided tothe auxiliary cable 334 a by the forward and reverse power transmitters368, 369 as discussed hereinabove.

FIG. 5 is a functional block diagram of the light-weight remotedirectional coupler 345 according to an embodiment of the presentdisclosure. The light-weight remote directional coupler 345 measures oneor more properties of a microwave energy signal and includes thethrough-signal coaxial cable 345 a and the coupled coaxial cable 345 b.Each of the through-signal coaxial cable 345 a and the coupled coaxialcable 345 b includes an inner conductor 344 a, 344 b and an outerconductor 342 a, 342 b, respectively, formed in a coaxial relationshiptherebetween. The outer conductors 342 a, 342 b of the through-signalcoaxial cable 345 a and the coupled coaxial cable 345 b each include afirst slot 346 a and a second slot 346 b formed therein. The first andsecond slots 346 a, 346 b are formed to allow coupling between the twocables 345 a, 345 b.

The labels provided on each cable 345 a, 345 b correspond to standardmarking for a directional coupler with the input signal indicated asPort 1, the through signal indicated as Port 2, the forward coupledsignal indicated as Port 3 and the reverse coupled signal indicated asPort 4. As such, the through-signal coaxial cable 345 a connects to thecoaxial cable 334 a of the transmission line 334 on Port 1 and theantenna 332 on Port 2 and the coupled coaxial cable 345 b connects tothe remote forward mixer 363 on Port 3 (providing a forward coupledsignal thereto) and the remote reverse mixer 364 on Port 4 (providing areverse coupled signal thereto).

In one embodiment, the slots 346 a, 346 b are created by stripping awaypart of the outer conductor 342 a, 342 b on each cable 345 a, 345 b. Foreach slot 346 a, 346 b, half of the outer conductor 342 a, 342 b wasremoved thereby forming a half-cylinder opening at each slot 346 a, 346b. As illustrated in FIG. 5, the length of each slot 346 a, 346 b isindicated by a slot length “SL” and the spacing between the slots 346 a,346 b is indicated by the slot spacing “SS”.

The performance and/or operational parameters of the light-weight remotedirectional coupler 345 are a function of slot spacing “SS” and slotlength “SL”. The slot spacing SS is the distance between the inner edgeof each slot 346 a, 346 b and the slot length “SL” is the opening widthof each slot 346 a, 346 b. The slot spacing “SS” is related to thelength of one-quarter of the microwave signal wavelength. Simulationsperformed with varying slot spacing “SS” and varying slot lengths “SL”determined that modification of the slot spacing “SS” resulted in largevariations in the directivity. For example, in one simulation,modification of the slot spacing “SS” by as little as 0.5 mm resulted inchanges in the directivity. To prevent any bending or repositioning ofthe position of the cable 345 a, 345 b the sections containing the firstand second slots 346 a, 346 b are fixed with respect to each other andwith respect to the handpiece 336.

As illustrated in FIG. 5, the slots 346 a, 346 b are positioned aboutone-quarter of a wavelength (λ/4) apart (e.g., 5.5 cm at 915 MHz usingstandard RG 58 cable) to allow the forward power signal to add in phasein Port 3 and to add out of phase in Port 4. Similarly, the reversepower signal will add in phase at Port 4 and add out of phase at Port 3.As such, only the forward coupled signal remains on Port 3 and thereverse coupled signal remains on Port 4.

Simulations conducted with varying slot lengths SL resulted indirectivity between 25 dB and 42 dB with slot lengths between about 13mm and 15 mm. Obviously, variations in the slot spacing “SS” and theslot length “SL” may provide other variations and are within the scopeof the present disclosure.

Returning to FIG. 4B, exposing the inner conductors 344 a and 344 b, asdiscussed hereinabove, may result in an undesirable release of radiationfrom the handpiece 336. As such, a metallic shield 370 configured toencircle at least the first and second slots 346 a, 346 b may be addedto reduce and/or eliminate any undesirable radiation released from thehandpiece 336. In one embodiment, the metallic shield 370 is formed froma first shield member 370 a and a second shield member 370 b thatconnect together and form a tube-like the metallic shield 370.

Simulations conducted with a metallic shield 370 resulted in a reductionof the directivity to approximately 25 dB and a decrease in the couplingfactor between the through-signal coaxial cable 345 a and the coupledcoaxial cable 345 b.

In another embodiment, at least a portion of the remote RF sensor 260 billustrated in FIGS. 3, 4B and 4B and discussed hereinabove are formedwith microstrip or stripline construction. The construction may includea conducting strip and a ground plane separated by a dielectricsubstrate. The microstrip may include any portion of the remote RFsensor 260 b, 361 described herein including any one or more of theremote directional coupler 245, the oscillator 265, the power splitter266, the mixers 263, 264 and the power transmitters 268, 269.

One example of a directional coupler made in microstrip or striplineconstruction is a branch-line coupler. A branch-line coupler may beformed by two main transmission lines shunt-connected by two secondary,or branch, lines. The two main transmission lines and the two secondarylines form a geometry such that the four ports have a 90 degree phasedifference between the two input ports and two output ports of the twomain transmission lines.

In one embodiment, the circuitry housed in the handpiece 336 is formedof a microstrip circuit wherein the transmission cable 334 connects to afirst coaxial connector formed on the proximal end of the microstripcircuit and the shaft 338 connects to a second coaxial connector formedon the distal end of the microstrip circuit.

As various changes could be made in the above constructions withoutdeparting from the scope of the disclosure, it is intended that allmatter contained in the above description shall be interpreted asillustrative and not in a limiting sense. It will be seen that severalobjects of the disclosure are achieved and other advantageous resultsattained, as defined by the scope of the following claims.

1. (canceled)
 2. A radio frequency sensor coupleable to a microwaveantenna, the radio frequency sensor comprising: a directional couplerincluding: a first coaxial cable including a first pair of slots; and asecond coaxial cable including a second pair of slots, wherein the firstcoaxial cable and the second coaxial cable are in contact with eachother such that the first pair of slots and the second pair of slots arealigned; a first mixer configured to receive a forward power measurementsignal from the directional coupler; a second mixer configured toreceive a reverse power measurement signal from the directional coupler;and a remote sensing interface coupled to the first mixer and the secondmixer, the remote sensing interface configured to transmit at least oneof the forward power measurement signal or the reverse power measurementsignal to a microwave generator.
 3. The radio frequency sensor accordingto claim 2, wherein the remote sensing interface includes at least oneconductor configured to couple a microwave energy delivery device to amicrowave generator.
 4. The radio frequency sensor according to claim 2,wherein the remote sensing interface includes a wireless transceiverconfigured to transmit at least one of the forward power measurementsignal or the reverse power measurement signal to a microwave generator.5. The radio frequency sensor according to claim 2, further comprisingan oscillator configured to generate a carrier signal at a carriersignal frequency.
 6. The radio frequency sensor according to claim 5,wherein the first mixer is configured to generate an intermediateforward signal by mixing the carrier signal and the forward powermeasurement signal and the second mixer is configured to generate anintermediate reverse signal by mixing the carrier signal and the reversepower measurement signal.
 7. The radio frequency sensor according toclaim 2, wherein the slots of each of the first pair of slots and thesecond pair of slots are separated by about one-quarter of a wavelength(λ/4) of a microwave energy signal transmitted through the first coaxialcable.
 8. A microwave energy delivery system, comprising: a microwavegenerator configured to generate a microwave energy signal, themicrowave generator including a processing unit configured to adjust aparameter of the microwave energy signal; and a remote radio frequencysensor configured to couple to the microwave generator, the remote radiofrequency sensor including: a directional coupler including: a firstcoaxial cable including a first pair of slots; and a second coaxialcable including a second pair of slots, wherein the first coaxial cableand the second coaxial cable are in contact with each other such thatthe first pair of slots and the second pair of slots are aligned; afirst mixer configured to receive a forward power measurement signalfrom the directional coupler; a second mixer configured to receive areverse power measurement signal from the directional coupler; and aremote sensing interface configured to transmit at least one of theforward power measurement signal or the reverse power measurement signalto the microwave generator.
 9. The microwave energy delivery systemaccording to claim 8, wherein the processing unit is configured toadjust the parameter of the microwave energy signal based on at leastone of the forward power measurement signal or the reverse powermeasurement signal.
 10. The microwave energy delivery system accordingto claim 8, wherein the processing unit further includes a comparatorconfigured to compare at least one of a portion of the microwave energysignal, the forward power measurement signal, or the reverse powermeasurement signal.
 11. The microwave energy delivery system accordingto claim 8, wherein the processing unit includes a generator processingunit and a remote power coupler processing unit, the generatorprocessing unit is configured to control generation and delivery of themicrowave energy signal and the remote power coupler processing unit isconfigured to receive at least one of a portion of the microwave energysignal, the forward power measurement signal, or the reverse powermeasurement signal and to provide at least one of a portion of themicrowave energy signal, the forward power measurement signal, or thereverse power measurement signal to the generator processing unit. 12.The microwave energy delivery system according to claim 8, furthercomprising a microwave energy delivery device coupled to the microwavegenerator through the remote sensing interface.
 13. The microwave energydelivery system according to claim 8, wherein the remote sensinginterface includes a wireless transceiver configured to transmit atleast one of the forward power measurement signal or the reverse powermeasurement signal to the microwave generator.
 14. The microwave energydelivery system according to claim 8, wherein the remote radio frequencysensor further includes an oscillator configured to generate a carriersignal at a carrier signal frequency.
 15. The microwave energy deliverysystem according to claim 14, wherein the first mixer is configured togenerate an intermediate forward signal by mixing the carrier signal andthe forward power measurement signal and the second mixer is configuredto generate an intermediate reverse signal by mixing the carrier signaland the reverse power measurement signal.
 16. The microwave energydelivery system according to claim 15, wherein the slots of each of thefirst pair of slots and the second pair of slots are separated by aboutone-quarter of a wavelength (λ/4) of the microwave energy signaltransmitted through the first coaxial cable.